Inverter efficiency directly impacts the system's power generation and is a key metric of great concern to customers. Improving the conversion efficiency of power inverters is crucial.

How to Improve Inverter Efficiency

The only way to improve power inverter efficiency is to reduce losses. The primary losses in inverters come from power switching transistors such as IGBTs and MOSFETs, as well as magnetic components such as transformers and inductors. These losses are related to the current, voltage, and process used, as well as the materials used.

IGBT losses

Can be divided into conduction losses and switching losses. Conduction losses are related to the internal resistance and the current flowing through the component, while switching losses are related to the switching frequency and the DC voltage to which the component is subjected.

Inductor losses

Can be divided into copper losses and iron losses. Copper losses refer to losses caused by the resistance of the inductor coil. When current flows through the inductor coil, heating it, a portion of the electrical energy is converted to heat and lost. Since the coil is typically wrapped with insulated copper wire, this is also called copper loss. This can be measured to calculate the transformer's short-circuit impedance. Iron losses include hysteresis losses and eddy current losses, which can be calculated by measuring the transformer's no-load current.

Technologies for Improving Inverter Efficiency

Currently, there are three technical approaches to improving power inverter efficiency.

First, control methods such as space vector pulse width modulation (SVM) are used to reduce losses.

Second, the composition of silicon carbide materials is used to reduce the internal resistance of power devices.

Third, three-level, five-level, and multi-level electrical topologies and soft switching technology are used to reduce the voltage across power devices and lower their switching frequency.

1. Space Vector Pulse Width Modulation (SVPWM)

SVPWM is a fully digital control method with advantages such as high DC voltage utilization and ease of control. It has been widely used in power inverters. High DC voltage utilization allows for the use of a lower DC bus voltage for the same output voltage, reducing voltage stress on power switching devices and switching losses, thereby improving the conversion efficiency of power inverters to a certain extent. In space vector synthesis, there are many combinations of vector sequences. By using different combinations and sequencing, the number of switching cycles of power devices can be reduced, further reducing the switching losses of power inverter power devices.

2. Components Made of Silicon Carbide

Silicon carbide devices have an impedance per unit area of only one hundredth that of silicon devices. Power devices such as IGBTs (insulated gate bipolar transistors) made of silicon carbide can reduce on-resistance to one-tenth that of conventional silicon devices. Because silicon carbide technology effectively reduces the reverse recovery current of diodes, it also reduces switching losses in power devices and the required current capacity of the main switch. Therefore, anti-parallel diodes using silicon carbide diodes as the main switch are a way to improve power inverter efficiency. Compared with traditional fast-recovery anti-parallel diodes, anti-parallel diodes made of silicon carbide can significantly reduce reverse recovery current, improving overall conversion efficiency by 1%. Using fast IGBTs can increase overall conversion efficiency by 2% due to the increased switching speed. Combining SiC anti-parallel diodes with fast IGBTs further enhances power inverter efficiency.

3. Soft Switching and Multilevel Technology

Utilizing the principle of resonance, soft switching technology allows the current or voltage in the switching device to vary according to a sinusoidal or quasi-sinusoidal pattern. When the current naturally crosses zero, the device turns off; when the voltage naturally crosses zero, the device turns on, reducing switching losses and addressing the issues of inductive disconnection and capacitive open circuits. Furthermore, when the voltage across the switch or the current flowing through it is zero, there is no switching loss, and the switch is either on or off. Three-level power inverters are primarily used in high-voltage, high-power scenarios. Compared to traditional two-level structures, they offer increased zero-level output and halve the voltage stress on power devices. For this reason, three-level inverters can utilize smaller output filter inductors than two-level inverters at the same switching frequency, effectively reducing inductor losses, cost, and size. Furthermore, for the same output harmonic content, three-level inverters can utilize lower switching frequencies, lower switching losses, and higher conversion efficiency than two-level inverters.